1. Field of the Invention
This invention relates generally to medical diagnostic imaging, and more particularly to the use of ultrasonic wave generation for early detection of cystic structures in the body, such as in the breast or ovary, the presence of which may indicate the onset of breast cancer or ovarian cancer.
2. Description of Background Art
Breast cancer is the most common cancer and the second most common cause of cancer-related death in women, with 175,000 cases and 43,700 deaths projected in 1999 in the United States. Ovarian cancer is the fourth leading cause of cancer-related death among females in the United States, with over 25,000 new cases in 1998 and approximately half that number in deaths. When diagnosed at an early stage, there is a very high likelihood of cure for both diseases; however, because of the location and usually asymptomatic nature of even relatively advanced ovarian cancer, this type of cancer exhibits a high morbidity and mortality rate. Moreover, current methods of breast screening with physical examination and mammography still miss a significant number of breast cancers detectable by ultrasonography.
The presence of multiple cysts and fibronodular structures make precise characterization and accurate follow-up by physical examination and mammography problematic. The complex nature of the fibrocystic breast in premenopausal women is a particular challenge to the diagnostician, which should be especially amenable to characterization by the present invention. Conventional ultrasonography is useful for examination of a focal region but is neither efficient nor reproducible from operator to operator or from visit to visit by the same operator.
Over two decades ago, there was a major effort to assess the value of whole breast screening using automated ultrasonography methodologies. Unfortunately, there were both high false-positive and false-negative rates. Nevertheless, later studies demonstrated that ultrasonography can detect, at least in radiologically dense breasts, cancers not recognized by mammography and physical examination. Recently, one study found by ultrasonography only three cancers per thousand when screening 6113 women with dense breasts and no symptoms and 687 women with palpable or mammographically detected masses. In commenting on these studies, Kopans (xe2x80x9cBreast Cancer Screening with Ultrasonography,xe2x80x9d Lancet 354 (9196):2096-7 (1999)) pointed out that although the independent rate of breast cancer detection by ultrasonography alone is not clear, the xe2x80x9cpossibility of ultrasonography for breast screening should not be ignoredxe2x80x9d. The author further noted that handheld devices are operator dependent and expensive, requiring significant time by a radiologist, and concluded that automated ultrasonography devices are needed, if only to evaluate the usefulness of ultrasonography in improving breast cancer detection.
The present invention provides such a device, with novel ultrasonography features making the method rapid, accurate, reproducible and capable of automation. The device can be constructed so as to be able to compare standard ultrasonography images with selective induction of ultrasonic cavitation (SINUC) generated images and distinguish cystic from non-cystic structures.
There has yet to be clinically identified any pre-malignant condition which would presage the onset of ovarian cancer. Because most ovarian cancers are cystic in nature, the recognition of an irregular, septate, fluid-filled lesion in the ovary has been the focus of detection by the medical community. Various imaging technologies, including positron emission tomography (PET), radioimmunoscintography, magnetic resonance imaging (MRI), compute tomography (CT) scanning, and ultrasonography, all are capable of detecting cystic structures in the ovary.
The recent addition of color flow Doppler imaging in combination with transvaginal sonography appears to have added another level of sensitivity to the detection of ovarian abnormalities. Cohen and Jennings (Am J Obstet. Gyncol; 170:1088-1094) report that endovaginal probes at frequencies of 6.5 to 7.5 MHZ provide much finer discrimination of the ovary and uterus than is achievable with transabdominal ultrasonography. However, the use of various antigen markers, in particular Ca 125, in combination with transabdominal and transvaginal sonography, or (in one study) magnetic resonance imaging, has failed to achieve the levels of sensitivity and specificity necessary for a highly reliable screening technique.
There thus exists a need for a more sensitive, specific, and affordable technique for early detection of ovarian and breast cancers.
The present invention provides a solution to the existing need in the art by providing a noninvasive technique for the early detection of cystic structures using ultrasonic waves, potentially at the levels of microns. The present invention is based on the fact that most ovarian cancers and many breast cancers are cystic in nature, consisting of fluid-filled lesions, and on the observation by the present inventors that for any given fluid (characterized in terms of density, ultrasonic wave velocity, and viscosity), there exists a characteristic resonance frequency or frequency range and a threshold ultrasound power level at which cavitation bubbles are formed.
These cavitation bubbles are produced during the rarefaction phase of the ultrasonic wave, and implode to release shock waves at the pressure phase. The diameter of the cavitation bubbles depends upon the wavelength of the ultrasonic emission, and in the range of approximately 500 kHz it is on the order of several microns.
The induction of cavitation and the detection of the resulting implosion waves can be carried out transabdominally and noninvasively through the skin. The location of the cavitation source producing the implosion wave can be identified and used to create a three-dimensional image of the cystic fluid structure. The diagnostic procedure according to the invention is rapid, with minimum inconvenience to the patient, thus providing an affordable screening technique.
In particular, the present invention provides a method for identifying the presence of cystic structures in any tissue. A first specific application of the invention is as a method for recognizing the presence of cystic structures including ovarian cancers in the ovary. The method includes the steps of applying ultrasonic wave energy to a patient at a frequency causing induction of cavitation in cystic fluid characteristic of cancerous and other cystic structures in the tissues of humans, such as ovarian tissue, detecting implosion waves caused by the implosion of cavitation bubbles formed by the induction of cavitation, measuring the detected implosion waves, and determining the location of the cavitation source in the body of the patient. A second specific application of the invention is using SINUC to map cystic structures in the radiologically dense breast.
According to another aspect of the invention, apparatus for performing the method of detection of cystic structures is provided.